1. Field of the Invention
The present invention relates to a novel gene. In particular, the present invention relates to a novel gene in plants which encodes a protein having the function of controlling an in-vivo signal transduction system in a physiological reaction system against brassinosteroid hormone.
2. Description of the Related Art
Transposons are mutagenic genes which are known to be ubiquitous in animal, yeast, bacterial, and plant genomes. Transposons are classified into two classes, Class I and Class II, depending on their transposition mechanisms. Transposons belonging to Class II are transposed in the form of DNAs without being replicated. Known Class II transposons include the Ac/Ds, Spm/dSpm and Mu elements of Zea mays (Fedoroff, 1989, Cell 56, 181–191; Fedoroff et al., 1983, Cell 35, 235–242; Schiefelbein et al., 1985, Proc. Natl. Acad. Sci. USA 82, 4783–4787), and the Tam element of Antirrhinum majus (Bonas et al., 1984, EMBO J., 3, 1015–1019). Class II transposons are widely used for gene isolation techniques which utilize transposon tagging. Such techniques utilize the fact that a transposon induces physiological and morphological changes when inserted into genes. The affected gene can be isolated by detecting such changes (Bancroft et al., 1993, The Plant Cell, 5, 631–638; Colasanti et al., 1998, Cell, 93, 593–603; Gray et al., 1997, Cell, 89, 25–31; Keddie et al., 1998, The Plant Cell, 10, 877–887; Whitham et al., 1994, Cell, 78, 1101–1115).
Transposons belonging to Class I, also referred to as retrotransposons, are replicated and transposed via RNA intermediates. Class I transposons were first identified and characterized in Drosophila and in yeasts. However, recent studies have revealed that Class I transposons are ubiquitous in plant genomes and account for a substantial portion of the genomes (Bennetzen, 1996, Trends Microbiolo., 4, 347–353: Voytas, 1996, Science, 274, 737–738). A large majority of retrotransposons appear to be inactive. Recent studies indicate that some of these retrotransposons are activated under stress conditions such as injuries, pathogenic attacks, or cell culture (Grandbastien, 1998, Trends in Plant Science, 3, 181–187; Wessler, 1996, Curr. Biol. 6, 959–961; Wessler et al., 1995, Curr. Opin. Genet. Devel. 5, 814–821). Activation under stress conditions has been reported for Tnt1A and Tto1 in tobacco (Pouteau et al., 1994, Plant J., 5, 535–542; Takeda et al., 1988, Plant Mol. Biol., 36, 365–376), and Tos17 in rice (Hirochika et al., 1996, Proc. Natl. Acad. Sci. USA, 93, 7783–7788), for example.
The Tos17 retrotransposon of rice is one of the most-extensively studied plant Class I elements in plants. Tos17 was cloned by an RT-PCR method using a degenerate primer prepared based on a conservative amino acid sequence in reverse transcription enzyme domains between Ty1-copia retroelements (Hirochika et al., 1992, Mol. Gen. Genet., 233, 209–216). Tos17 is 4.3 kb long, and has two 138 bp LTRs (long chain terminal repetitions) and PBS (primer binding sites) complementary to the 3′ end of the start methionine tRNA (Hirochika et al., 1996, supra). Tos17 transcription is strongly activated through tissue culture, and its copy number increases with culture time. In Nipponbare, a model Japonica cultivar used for genome analysis, two copies of Tos17 are initially present, which are increased to 5 to 30 copies in a regenerated plant after tissue culture (Hirochika et al., 1996, supra). Unlike Class II transposons which were characterized in yeasts and Drosophila, Tos17 is transposed in chromosomes in random manners and causes stable mutation, and therefore provides a powerful tool for functional analysis of rice genes (Hirochika, 1997, Plant Mol. Biol. 35, 231–240; 1999, Molecular Biology of Rice (ed. by K. Shimamoto, Springer-Verlag, 43–58).